Gallium Nitride (GaN) devices show great promise for next-generation high-power RF and high-voltage applications. However, for many applications, leakage currents are a significant concern. While many process, epitaxial, and design parameters can have an impact on the magnitude of leakage current, a gate metal stack typically used with GaN devices plays a critical role in the management of leakage current. A gold (Au) layer disposed on the GaN gate surface has been found to be a significant factor in driving leakage. Thus, the gate stack, which usually contains Au for RF devices, will need an effective diffusion barrier to prevent the Au from reaching the surface. Therefore, a need remains for a semiconductor device with reduced leakage current and a method for making the same.